1. Technical Field
This invention relates generally to displays for decorative, advertising, and other promotional purposes, and more particularly to a rotating display apparatus powered by the wind for rotation about a vertical axis.
2. Description of Related Art
A rotating display apparatus (RDA) displays decorative objects, advertising, or other information as it rotates. An RDA that rotates about a vertical axis falls under the general description of a vertical axis wind turbine (VAWT), and a VAWT fits into one of two categories: either it has a fixed or rigid rotor structure, or it has movable members, reactive elements, airfoils, vanes, or the like. Many VAWTs in the first category, those with a fixed or rigid rotor structure, are derivations of the roof ventilator. Others of that category are adaptations of the basic xe2x80x9cSxe2x80x9d shape with typically two or three, but potentially up to six, sides or facets.
VAWTs in the second category, those with movable members and so forth, are either proactive or reactive. The airfoils or elements of a proactive VAWT are positioned in relationship to the wind via gears, cams, cables, pulleys, rods, or any number of other means in order to produce lift and turn the rotor. To accomplish this, the system must be aware of the wind direction, which is usually accomplished by means of a weathervane-type mechanism. One characteristic of this design type is the typically symmetrical angle of attack profile of the elements, usually configured for crosswind lift on the windward and leeward portions of the cycle, and faired on both the downwind and upwind legs. Pros and cons of this approach are described in U.S. patent application Ser. No. 10/178,209.
In a reactive VAWT, the airfoils or elements position themselves in response to fluid pressures experienced locally. These forces are produced by a combination of the true wind and the relative wind created by rotation. Some existing RDAs are this type. U.S. Pat. No. 482,178, for example, describes an advertising device that uses weights on a curved horizontal member, like a tightrope walker uses a balance bar. At each end of the horizontal member is a xe2x80x9cpackagexe2x80x9d (e.g., a medicine bottle) and support for a vane, hinged on its edge by a thin vertical support, which allows the down-wind vane to swing outward and catch the airflow, and the upwind vane to swing back to reduce friction. The patent illustrates the large supporting base of the unit echoing the xe2x80x9cpackage.xe2x80x9d This is a simple mechanism, but it is probably as effective as some more complicated versions. This device appears to be intended to support specific products as the xe2x80x9cpackagesxe2x80x9d and base structure would be uniquely shaped in manufacturing. No accommodation for a generic version capable of supporting a range of xe2x80x9cpackagesxe2x80x9d is suggested.
U.S. Pat. No. 704,002 describes a wind actuated advertising device that is a bit more complicated, but basically a version of the advertising device discussed above. The vanes are hinged near the one-third point, but no mention is made of balancing them around the pivot point. A single-function spring dampener is attached to each radial arm, allowing the vanes to rotate freely until contacting the dampener finger along the radial position of the hub arm, on either side of the element. Functionality of the vanes is such that the downwind vanes will swing out to catch the airflow and the upwind vanes will fare into the wind. The spring mechanism would be called upon to dampen the potentially violent transitional movements of the vanes.
U.S. Pat. No. 1,232,895 describes a revolving sign. The airfoil-shaped elements are not damped or constrained in any manner, and movement is produced in a rather random and haphazard way by independent movement of the elements in reaction to changes in wind direction and speed. Being unconstrained, all the elements will align simultaneously with the wind. The description suggests that the device be put near a window with an electric fan blowing on itxe2x80x94perhaps in order for the interference between the fan and the outside wind to cause the device to move. The intent is obviously for the display of advertising as opposed to a continuously rotating mechanism.
U.S. Pat. No. 1,511,965 describes an advertising device that uses simple flat elements that swing broadside to the wind in the downwind phase and swing outward to streamline into the wind on the upwind leg. Several armature configurations a represented. The most obvious feature of this design is its unbalanced nature. A great deal of strain will be encountered in the main pivot point and support structure, and the elements that swing outward will momentarily flail wildly in the wind. Centrifugal force will also take a toll in swinging the panels into the windxe2x80x94acting as an effective brake. This type of system would tend to run very sporadically, in fits and starts.
U.S. Pat. Nos. 1,534,634 and 1,534,635 describe a wind sign that is similar to the revolving sign described in U.S. Pat. No. 1,232,895 in that the elements rotate freely and independently. Based upon the description (i.e., xe2x80x9c. . . it has been found by actual use of the device that all of the vanes will point in substantially the same direction when subjected to the wind, and the pressure of the wind upon the vanes causes the rotatable frame to rotate slowly . . . xe2x80x9d), if all the vanes point simultaneously into the wind, there is no imbalance of forces to produce rotation. The patent presents information on the panels, without considering the aerodynamic principles that would permit the unit to revolve consistently.
U.S. Pat. No. 2,030,769 describes an advertising device that uses drag downwind and fairing upwind and is closely similar to the advertising device described in U.S. Pat. No. 1,511,965 discussed above. Because of the way the figures are illustrated, and the fact that the units are shown rotating in opposite directions, this is not immediately obvious. It will be subject to the same balance issues and performance shortcomings of the earlier design.
U.S. Pat. No. 2,076,784 describes a display device, of the xe2x80x9croof ventilatorxe2x80x9d type, that is mentioned here because it shows the presentation of a three-dimensional object. U.S. Pat. No. 3,292,319 describes a sea gull guard, with a different intended use, but one version shown gives an example of reactive elements being used to produce crosswind lift exclusively. FIG. 4 in that patent shows a rotating apparatus with reactive elements (vanes) constrained between a ninety degree free movement range, with the downwind drag phase (startup power) being inefficient due to the forty-five offset of the vane. However, since the unit is intended to be used in areas of steady wind (e.g., marinas) and given its long moment arm, lightweight mass, and low wind resistance mounting radial, self-starting issues should not be a concern.
The foregoing illustrates that none of the prior art device reviewed above explore the concept of accommodating shaped, two-dimensional or three-dimensional reactive elements and the use of standardized mounting features for easy interchangeability. In addition, none address mechanisms for avoiding storm damage and most appear vulnerable to high winds. Furthermore, none of the devices address means of adjusting element position or optimizing efficiency. Although not a top priority, higher efficiency translates into better performance at lower wind speeds. Moreover, none of the devices use the five-phase movement described in U.S. patent application Ser. No. 10/178,209.
The two most common approaches in the prior art reviewed above are (a) drag 180 degrees, fair 180 degrees, and (b) crosswind lift only. For the first approach, the elements in the above designs rotate 180 degrees on their axes, create drag thrust on the downwind phase, and use some strategy to reduce the drag on the upwind leg. Units using this approach tend to turn more slowly, but start more easily, than lift-only designs. For the second approach, the reactive elements in the above designs typically rotate 90 degrees or 45 degrees both sides of a line perpendicular to the radial arm. These systems do not have the high-torque start-up characteristics of the drag-only designs, but once started tend to rotate faster. Thus, existing RDAs have some drawbacks that need to be overcome, and so a need exists for an RDA that overcomes those concerns, preferably an RDA incorporating benefits of modern aerodynamic design and performance theory.
It is an objective of this invention to overcome the forgoing and other disadvantages of prior art rotating display devices. This object is achieved by providing a rotating display apparatus (RDA) having xe2x80x9cfree flyingxe2x80x9d wind-reactive elements that self position according to the local dynamic conditions to which they are subjected, thus creating a condition of equilibrium under which a highly efficient means of wind energy extraction may be established. More particularly, the RDA includes a rotor mounted on a support structure for rotation about a vertical rotational axis. At least two wind-reactive elements (airfoils or non-airfoils) mounted pivotally on the rotor (preferably more than two) cause the rotor to rotate under influence of the wind. The wind-reactive elements are mounted on the rotor so that they are free to pivot between first and second pairs of stop positions (i.e., preset first and second limits of pivotal movement set by stop mechanisms). That arrangement enables the wind-reactive elements to align according to the wind as they orbit the rotational axis, thereby achieving better conversion of wind energy to useable rotational energy during five phases of each revolution.
The dynamic phase lag effect of the free flying wind-reactive elements creates a xe2x80x9cvirtual stop.xe2x80x9d Recall the Law of Conservation of Angular Momentum and consider its influence in combination with airfoil responsiveness to the instantaneous force of the true relative wind (TRW) acting on an airfoil. The result is that the wind-reactive elements resist rotational changes along their pivotal axes and shift out of phase relative to rotor position. That is what the stop mechanisms do also. The stop mechanisms cannot be completely eliminated, however, because they are required during start-up, operation at low speed, heavy load conditions, turbulence, and wind direction shifts requiring reorientation and stabilization of the system. The stop mechanisms are important in getting the system up to equilibrium speed.
To paraphrase some of the more precise language appearing in the claims and introduce the nomenclature used, a rotating display apparatus constructed according to the invention includes a support structure, a rotor mounted rotatably on the support structure for rotation about a vertically disposed rotational axis, and at least two wind-reactive elements on the rotor on which a user may display information or mount ornamental shapes. The wind-reactive elements function as means for causing the rotor to rotate about the rotational axis in response to wind passing the rotating display apparatus.
The two wind-reactive elements include a first wind-reactive element that has a first leading edge and a first trailing edge, a first central axis extending horizontally through the first leading edge and the first trailing edge, and a pivotal axis extending vertically intermediate the first leading edge and the first trailing edges. The first wind-reactive element is mounted on the rotor for pivotal movement about the first pivotal axis between a first pair of stop positions. The two wind-reactive elements also include a second wind-reactive element that has a second leading edge and a second trailing edge, a second central axis extending horizontally through the second leading edge and the second trailing edge, and a pivotal axis extending vertically intermediate the second leading edge and the second trailing edge. The second wind-reactive element is mounted on the rotor for pivotal movement about the second pivotal axis between a second pair of stop positions.
According to a major aspect of the invention, each of the first and second wind-reactive elements is mounted on the rotor so that each of the first and second wind-reactive elements is free to pivot between a respective one of the first and second pairs of stop positions as the rotor rotates about the rotational axis. That arrangement enables the wind-reactive elements to align their central axes continually according to the wind and impart rotational movement to the rotor as they orbit the rotational axis. Although the device has demonstrated the capability of starting and running with one element only, preferably, the RDA has more than two wind-reactive elements. Variable stops and constrictive dampening mechanisms may be employed that can provide better efficiency and protection in heavy wind conditions.
In terms of its many advantageous design features, the RDA of the invention uses two or more self-positioning wind-reactive elements that achieve better conversion of wind energy to useable rotational energy. The RDA needs no cams, gears, levers, or other mechanisms to position the wind-reactive elements, thereby reducing design complexity, minimizing frictional overhead, and increasing working efficiency. The energy transfer cycle is optimized by the application of aerodynamics based on airplane and helicopter airfoil flying and stalling characteristics and the physics of conservation of rotational energy. T he wind-reactive elements optimize each phase in the rotational cycle, using four distinct methods of applying motive force to the rotor armature.
Wind forces and armature-constraining action alone establish wind-reactive element positions. The wind-reactive elements rotate freely through a maximum arc of approximately 90 degrees, bounded by stop mechanisms. The wind-reactive elements"" span of travel is from a radial line along the mounting arm (radially aligned relative to the vertical rotational axis) to a perpendicular position (tangentially aligned relative to the rotational axis). The design allows for each wind-reactive element to set its own instantaneous angle and to adjust to conditions of relative wind, wind shift, and so forth occurring outside and within the RDA, without external adjustments or mechanisms, wind vanes, or other controlling devices. Individual wind-reactive elements adjust to local conditions based on changes of rotor speed, turbulence, true relative wind, and other factors affecting each of them independently.
The RDA design is scalable, both in terms of overall size and in terms of the number of wind-reactive elements utilized. It may be configured in a smaller radius for higher RPM operation, or larger diameter for lower RPM operation and higher torque. The RDA design allows for easy aesthetic placement in the landscape.
The RDA design employs a five-step sequence:
1. Upwind Lift Phase. This begins approximately in the upwind position and continues to approximately 60 degrees past it, depending on wind and rotor speed conditions.
2. Downwind Drag Phase. This begins at approximately 60 degrees downwind and continues to around the 120 degree position.
3. Transitional Phase. At about the 120 degree position, the airfoil rotates its orientation by 90 degrees and converts its rotational energy into rotor thrust by the law of conservation of rotational inertia.
4. Leeward Lift Phase. Positioned crosswind by the transitional phase, the wind-reactive element now sweeps across the leeward side of the system.
5. Upwind Phase. The wind-reactive element returns to windward, positioning itself for minimum drag.
Thus, the rotating display apparatus (RDA) of this invention provides significantly improved performance, mechanical attributes, and aesthetics. The design has the ability to utilize both drag and lift forces. This allows the device to rotate in very low and unstable wind conditions, using drag forces alone, which is an advantage to a device that may be mounted near the ground for decorative purposes. This high-torque capability also enables it to support elements that are relatively non-aerodynamic, unbalanced, or even three-dimensional (i.e., not flat). The device is also capable of running smoothly and efficiently in stronger, cleaner wind, in applications where it might be mounted on a pole or roof-top, using lift forces or a combination of lift and drag forces. Various auxiliary mechanisms may be applied to the device to improve its efficiency, enhance its operational smoothness, and protect it from the damage of high winds. The design allows for easy change and replacement of wind-reactive elements and dampeners. The following illustrative drawings and detailed description make the foregoing and other objects, features, and advantages of the invention more apparent.